Security and room monitoring systems typically employ some combination of door and window opening detectors and PIRs. These devices are connected to a central processing alarm panel located somewhere within the building. A PIR can be used as a type of motion detector that uses invisible infra red light to detect movement in a room. Prior art PIRs have detector elements that generate electrical pulses when movement is detected. By integrating the pulses over a predetermined time period, the PIR makes a determination as to when to trip an alarm. When it is determined that an alarm is tripped, the PIR sends an alarm signal to the central processing alarm panel which in turn processes the alarm to alert a central monitoring station, energize a horn, etc. Other than simple components to integrate pulses to generate an alarm signal, current PIRs do not include any “intelligence.” Put another way, because it is typically desirable to make the PIRs as inexpensive as possible, PIRs typically do not include microcontrollers, digital signal processors or any other components needed to generate more than a simple alarm trigger.
As is shown in FIG. 1, PIR detectors 10 used for motion detection often use either a Fresnel lens or a segmented mirror 12 to focus the infrared radiation onto the detector element 14. The lens or mirror (referred to collectively herein as a “lens”) 12 may also be divided into zones 16 such that movement through the detection region causes an output pulse from the detector element 14 for movement through each zone 16. A lens may typically have 15 to 20 segments/zones. As such, a person crossing the detection region results in the generation of a series of pulses by the detector element 14 consistent with the number of zones the lens has. As is shown in FIG. 1, typical multi-segment lenses employ segments that are the same width. This results in the generation of equally timed pulses if the person traversing the sensor moves at a constant rate. Although the series of pulses may be integrated to establish an alarm, the pulses emanating from the detector do not indicate which direction the person is moving because the lens segments and resultant zones 16 are of equal width.
In order to provide information that is more useful than simply whether a PIR has been tripped via the transmission of a simple alarm signal to a central alarm panel, it is desirable to know which direction the person tripping the alarm was moving. In other words, it is desirable to have vector information in addition to the mere alarm trip signal. Such information can be useful, for example, in determining whether the person tripping the alarm was moving into or out of a room, the direction through a doorway, up or down, etc. Such information can also be used to enable cameras in the projected path of movement, verify the alarm to cut down on false alarm indications, etc.